[Bug middle-end/83215] C++: struct with char-array assumed to alias with everything

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83215

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |alias, missed-optimization
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2018-11-16
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So in the end it is

tree
component_uses_parent_alias_set_from (const_tree t)
{
...
      if (get_alias_set (TREE_TYPE (TREE_OPERAND (t, 0))) == 0)
        found = t;

that causes this.  The above is required for may_alias annotated types
(so history tells me, but the testcase added for the change doesn't fail
when removing the above).  Today we handle may_alias via
reference_alias_ptr_type_1 running into a dereference and checking the
pointer for a ref-all type.